brainpopfandomcom-20200223-history
Dams/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby A boy, Tim, and a robot, Moby, watch a beaver with a wooden stick in his mouth swim to a dam he is building in a river. TIM: Yeah, they're cute. The beaver is gnawing a tree trunk. Tim reads from a typed letter. TIM: Dear Tim and Moby, What does a dam do? From, Kinzi. MOBY: Beep. Moby giggles. TIM: Oh, stop, she means the things in rivers. Dams have been used to block the flow of rivers and waterways for thousands of years. In ancient Iraq and Egypt, dams were built to irrigate dry farmlands. Dams are still used for irrigation, bringing water to dry land areas. An image shows a dam being used to irrigate dry land. TIM: Today, they are also used to generate electricity, control flooding, deepen waterways for shipping, and the collection of drinking water. Images illustrate the uses of dams that Tim describes. TIM: Dams can be anywhere from a couple feet to hundreds of feet high. Side by side animations show the small dam the beaver built and a large dam. TIM: Actually, it's not all that complicated. Dams block up a river's channel, causing water to accumulate upstream or behind the dam. The accumulated water forms an artificial lake, or reservoir. An animation shows how a dam works and how a reservoir forms. TIM: People can then release the water whenever they want, either through aqueducts, or water pipes, leading away from the reservoir or through gates in the dam itself, letting the water flow back into the river bed. The animation shows the aqueducts and gates. When the gates open, the water flows through and down into the river bed. TIM: If a river floods a lot, damming it helps put water flow under human control. And rivers with a heavy flow can be harnessed for hydroelectricity. An image shows water from a reservoir being used to generate hydroelectricity. MOBY: Beep. TIM: Well, when the water from a hydroelectric dam's reservoir is released, it flows past a special engine called a turbine. An image shows a turbine. TIM:The moving water turns the turbine blades, and the motion is converted into electricity. An animation shows electricity flowing from the turbine engine through electric power towers. TIM: Big hydroelectric dams, like the Grand Coulee Dam in Washington state, generate enough electricity to power entire cities. An animation shows the Grand Coulee Dam. MOBY: Beep. TIM: Yeah. Irrigation, clean electricity, flood control, dams can be really useful. But they also can do serious damage to the environment. Dams interrupt the lifecycle of fish who depend on swimming up and downstream, like salmon. An animation shows a salmon swimming upstream, bumping into a dam, and dying. TIM: And reservoir water released back into a riverbed is often much colder than normal. That can make the rest of the river unlivable for the animals there. An animation shows fish swimming on the downstream side of the dam and dying from the cold water from the reservoir. TIM: Dams can also prevent the usual flow of nutrients down a river, starving the ecosystems downstream. The animation shows dead river plants in the river downstream. The reservoir water upstream turns green. MOBY: Beep. TIM: Well, there are solutions to some of these problems. A lot of dams have fish ladders built into their sides, allowing fish to get around them. An animation shows a fish ladder on the downstream side of the dam. A fish swims and jumps to the higher water using the ladder like steps, and jumps over the dam to swim upstream. TIM: And reservoir water can be heated as it's released from a dam. An animation shows water flowing from a reservoir through heaters in the dam's gate. Moby and Tim are standing in the river in knee-deep water. The beaver swims by with a stick in his mouth, and holds onto Moby's leg. TIM: Come on. Let's get out of here before you rust. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts Category:BrainPOP Engineering & Technology Transcripts